Solid-state burglar alarm detector

ABSTRACT

A burglar alarm detector including a silicon controlled rectifier which is triggered to activate alarm means by means of coupling means included in the input circuit thereof, which coupling means is, in turn, responsive to a predetermined condition of a protective circuit.

United States Patent [72] Inventor Clifford Howard Uthene [56] References Cited m UNITED STATES PATENTS g Qfg' g 3,041,592 6/1962 Schmidt 340/276 x pawmed 3,286,250 11 1966 Teitelbaum 340/276 [73] Assignee Chicago Fire and Burglar Detection. he. 3,425,050 1/1969 Tellerman et al 340/280 X Glen Ellyn, lll. Primary Examiner-John W. Caldwell Assistant Examiner-Scott Partridge A!t0rneysCarl J. Greenberg and Dominin, Knechtel and [54] SOLID-STATE BURGLAR ALARM DETECTOR Godula 3 Claims, 2 Drawing Figs.

[52] US. Cl 340/276,

340/274 ABSTRACT: A burglar alarm detector including a silicon con- [51] Int. Cl G08b 13/00, trolled rectifier which is triggered to activate alarm means by G08b 1 3/08 means of coupling means included in the input circuit thereof, [50] Field of Search 340/276, which coupling means is, in turn, responsive to a predeter- 280, 227, 420, 274; 307/85, 252 mined condition ofa protective circuit.

PATENTED JULZOISYI 3594.771

I: 1 v1; ."1 UR. 1i ford H. Ufhene Arty.

SUiLlilDJ-STATE idllllilGlLAl l ALAi'lln'i This invention relates to a burglar alarm signal detecting device and, in particular, to an alarm signal detecting device utilizing solid state switching elements.

It has long been common in the burglar alarm art to utilize a relay as the means for detecting an interruption in the protective alarm circuit, and consequently, upon the "dropout" of the relay to actuate the alarm. However, such a relay actuated system has certain inherent limitations. The chief disad vantage is the constant current drain from the battery source to lock-in" the relay. This current drain, even for very sensitive relays, will eventually cause the protective circuit battery to fail, and hence, the system to falsely actuate. To guard against such failure, it is common practice to replace the batteries periodically, thereby incurring both the repeated expense of service calls and the replacement cost of the batteries.

Another limitation of such a system is the sensitivity of the relay to "drop-out" due to environmental factors. That is, vibration and mechanical shoclts in the vicinity of the alarm installation have been known to cause the relay to "dropout", thereby falsely actuating the alarm. in addition, since a relay is essentially a low impedance device, the detecting system is sensitive to relatively small changes in the total resistance of the protective alarm circuit, which changes can cause the alarm ultimately to be falsely actuated. This is an important consideration in those installations where the environmental atmosphere contains corrosive or oxidizing agents. False actuation of the alarm system from any of these causes results in an expensive and inconvenient service call, generally at night or on weekends when the system is in operation. The present invention is specifically designed to greatly minimize these deficiencies and limitations in prior burglar alarm equipment.

For most installations of burglar alarm systems in commerciul or industrial facilities, insurance underwriters require merits specify the use of DC battery powered alarm systems so I that the system is independent of and uncffected by outages in the commercial AC power source. However, in some of these installations, such as where there is extensive refrigeration equipment, it is highly desirable for the alarm system to be actuated by the loss of AC power to the entire facility, or the loss of AC power to a particularly crucial machine. The advantages of having the same burglar alarm signal detector be capable of operating with either an AC or a DC signal in the protective circuit without any modifications or changes in the detector circuitry is, of course, obvious.

Accordingly, it is an objective ofthis invention to provide an alarm detecting device which is equally sensitive to either a DC or an AC alarm signal.

It is another object of this invention to provide an alarm detecting device which utilizes negligible current drain from the protective circuit batteries.

Another objective of this invention is to provide a detecting device which has a very high degree of reliability.

Another objective of the invention is to provide a detecting device which is insensitive to large changes in the resistance of the protective system.

A further objective of the invention is to provide an alarm detection device which is insensitive to changes in environmental conditions, such as shock, vibration, temperature, humidity, dirt, dust, or corrosive agents in the environmental atmosphere.

Another object of this invention is to provide at detecting device which is simple to manufacture and hence relatively inexpensive.

A still further object of this invention is to provide a detection device which can be hermetically sealed in epoxy material, thereby becoming relatively tamper-proof and immune from changes in environmental conditions.

A feature of this invention is the use of solid-state devices to detect interruptions in the protective circuit.

A further feature of this invention is the ricgligibh' current drain from the alarm system batteries whereby battery life is essentially equal to the shell life of the batteries.

These and other objectives and features, which will become apparent from the following description and drawings, are accomplished by means hereinafter described and claimed. The invention is described hereinafter in detail without attempting to show all of the various modifications by which the invention may be practiced, the invention being measured solely by the appended claims.

FlG. ii is a schematic wiring diagram of a circuit for detecting an alarm signal, exemplary of the present invention. FlG. 2 is a continuation of the embodiment of the invention shown in Flt l, but specially adapted for remote signally such as in a central station alarm system.

The general combination of the components of the burglar alarm detecting device is illustrated in Fit}. 1. The input terminals 2 and 3 ofdetccting device l are connected to the protective circuit 4 which consists of a dry cell battery 5 con nected in series with a plurality of directly actuated sensors 6, such as microswitches or window casement tapes.

input terminals 2 and 3 are shunted by capacitor i3 while terminal 2 is bypassed to a ground connection through capacitor i l. Terminal 2 is also connected through choltc H5 to the emitter Jill oftransistor H, which is connected as a diode, with its collector l9 directly tied to base 2t), and which is bypassed by capacitor 23. The input circuit is completed from base 2d of transistor l? to terminal 3 through coupling resistor 2i, which is shunted by filter capacitor 22, and choice iii.

Coupling resistor is also connected in parallel with a second, or control, circuit comprising dry cell battery 23, the gate-cathode junction of silicon controlled rectifier 32, re sistor 2% and base-emitter junction of transistor 24-, which is connected as a diode with its collector an tied to base 27, and which is bypassed between its emitter 25 and its base 2'7 by capacitor 2%. Cathode 33 and gate 34 of rectifier 32 are bypassed by capacitor 30. Rectifier 32 is connected through its cathode-anode junction path to vibrating alarm bell 42, which is in parallel with load resistor 39, diode and battery 3'7. The cathodcanode junction of rectifier 32 is bypassed by capacitor 36.

When protective circuit 4 is made operative, i.e., all actuated sensors 6 are in a closed condition, the voltage potential across coupling resistor 21, resulting from the current flow in protective circuit 4, is transferred through transistor 24 and resistor 29 to bias gate 34 with respect to the gate cathode junction of silicon controlled rectifier 32. The bias applies to the gate-cathode junction prevents this rectifier from conducting current through its cathode-anode circuit.

When a sensor 6 in protective circuit 4i is opened, the current through protective circuit 4 is, of course, reduced to zero, thereby reducing the voltage drop across coupling resistor 21. The bias potential across the gatecathode junction of rectifier is correspondingly changed to that provided by only battery 23, which bias is of such a magnitude as to insure rectifier 32 to heavily conduct current, provided by battery 37, through its cathode anode circuit. Rectifier 32 remains in a conducting state, thereby continually actuating vibrating alarm bell 42, through the DC path provided by load resistor 39, until the circuit is manually reset by means of switch 38. it is to be noted that if input terminals 2 and 3 are shorted by someone tampering with the burglar alarm system installation, the voltage drop across resistor 2] is likewise reduced, thereby causing rectifier 32 to conduct current.

The input circuit of detecting device 1, consisting, in part, of coupling resistor 21 and transistor 17, represents the return path for protective circuit 4 and presents a high impedance load to protective circuit 4. Due to the high impedance, not only is current flow in protective circuit 4 minimized but the effect of resistance changes in protective circuit 4 on the operation of detecting device 1 is also greatly minimized.

Transistor T7 not only prevents reverse current flow through protective circuit 4, but also acts at a half wave rectifier in conjunction with coupling resistor 21 and filter capacitor 22. That is, if alarm detector 1 is utilized to monitor an AC power source, transistor 17 rectifies the AC signal induced in protective circuit 4. For such an application, battery in protective circuit 4 must be replaced by the secondary winding of a stepdown transformer. The primary winding of the stepdown transformer is connected to the AC power source which is to be monitored. Preferably, the peak AC voltage induced in protective circuit 4 by the secondary winding of the stepdown transformer should be approximately equal to the voltage potential of battery 5.

The other elements in the input circuit, namely, chokes l5 and 16 and capacitor 13 and 14, constitute a double low-pass filter, whereby stray RF or transient signals induced in the long lead wire of protective circuit 4 are efficiently shunted to ground and thus will not effect the operation of alarm detecting device 1.

Capacitor 28 bypasses transistor 24 for stray AC and RF currents which might be induced in any part of the control circuit of alarm detector 1. Consequently, transistor 24 is prevented from rectifying stray AC and RF signals and is thus prevented from applying false triggering signals to the gatecathode junction of silicon controlled rectifier 32. Capacitors 30 and 36 bypass the gate-cathode and cathode-anode junctions, respectively, of rectifier 32 and effectively block any transient signals from falsely triggering rectifier 32.

The circuit diagram shown in FIG. 2 is a switching device 50 designed as a continuation of alarm detecting device 1 and adapted to impress a signal corresponding to that actuating alarm bell 42 on telephone lines, or the like, which are connected to output terminals 64 and 65, to a remote central alarm station. Terminals 40 and 44 are connected to the baseemitterjunction path of switching transistor 52 through a voltage divider network consisting of resistors 51, 57 and 58, respectively. The collector-emitter junction circuit for transistor 52 is completed through limiting resistor 62, the load at the central station connected through output terminals 64 and 65, and battery supply 63. Both base 53 and collector 54 of transistor 52 are bypassed by capacitors 56 and 61, respectively, to minimize transient responses. Base 53 is also connected to battery 63 through a voltage divider network, consisting of resistors 58 and 59, and resistor 57.

In the absence of a signal cross terminals 40 and 44, transistor 52 is in a normally conducting state caused by the bias applied to base 53 from battery 63 through the voltage divider network of resistors 58 and 59. When transistor 52 is in a conducting state, a voltage signal is applied across output terminals 64 and 65. The signal across output terminals 64 and 65 is, of course, transmitted through the connected telephone lines to the central station. When alarm bell 42 is rung, the alarm signal is impressed upon the base-emitter junction of transistor 52, thereby biasing the switching transistor to the nonconducting state. The absence of a voltage signal across terminals 64 and 65 is then sensed at the central station as an actuation of alarm detector 1. Diode 43 in alarm detector 1 prevents the input circuit of switching device 50 from being essentially shorted out by alarm bell 42 when alarm bell 42 is not activated.

It is to be noted that all of the components of alarm detector 1 and switching device 50 are capable of being hermetically sealed in epoxy, thereby greatly enhancing their resistance to any changes in environmental conditions. These components are also very resistant to mechanical shocks or vibrations in comparison with components, such as relays and vacuum tubes, which are normally utilized in prior art burglar alarm systems.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in the above construction without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense,

It 18 also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention, which, as a matter of language, might be said to fall therebetween.

Now that the invention has been described, what I claim as new and desire to be secured by Letters Patent is:

1. A burglar alarm detector for use with a protective circuit comprising a silicon controlled rectifier having a gate; an output circuit including a first source of power, alarm means and said silicon controlled rectifier connected in a series circuit whereby said alarm means is activated when said silicon controlled rectifier is rendered conductive; a second source of power normally impressing a bias potential on said gate to render said silicon controlled rectifier conductive; and an input circuit including said protective circuit, a third source of power and biasing means connected in a series circuit, said biasing means being coupled to said gate and impressing thereon a bias potential of a magnitude to override the bias potential of said second source of power to maintain said silicon controlled rectifier nonconductive, said biasing means being rendered inoperative when said protective circuit is inoperative, thereby permitting said second source of power to render said silicon controlled rectifier conductive.

2. The burglar alarm detector of claim 1, wherein said biasing means comprises resistance means connected in said series circuit with said protective circuit and said third source of power, the current flow through said input circuit when said protective circuit is operative developing a potential across said resistance means of a magnitude to override the bias potential of said second source of power and thereby maintain said silicon controlled rectifier nonconductive.

3. The burglar alarm detector of claim 1, wherein said input circuit further includes high impedance means which minimizes current flow in said input circuit and which minimizes the effect of resistance changes in said protective circuit on said detector whereby said detector utilizes negligible current drain from its source of power and is insensitive to large changes in the resistance of the said protective circuit. 

1. A burglar alarm detector for use with a protective circuit comprising a silicon controlled rectifier having a gate; an output circuit including a first source of power, alarm means and said silicon controlled rectifier connected in a series circuit whereby said alarm means is activated when said silicon controlled rectifier is rendered conductive; a second source of power normally impressing a bias potential on said gate to render said silicon controlled rectifier conductive; and an input circuit including said protective circuit, a third source of power and biasing means connected in a series circuit, said biasing means being coupled to said gate and impressing thereon a bias potential of a magnitude to override the bias potential of said second source of power to maintain said silicon controlled rectifier nonconductive, said biasing means being rendered inoperative when said protective circuit is inoperative, thereby permitting said second source of power to render said silicon controlled rectifier conductive.
 2. The burglar alarm detector of claim 1, wherein said biasing means comprises resistance means connected in said series circuit with said protective circuit and said third source of power, the current flow through said input circuit when said protective circuit is operative developing a potential across said resistance means of a magnitude to override the bias potential of said second source of power and thereby maintain said silicon controlled rectifier nonconductive.
 3. The burglar alarm detector of claim 1, wherein said input circuit further includes high impedance means which minimizes current flow in said input circuit and which minimizes the effect of resistance changes in said protective circuit on said detector whereby said detector utilizes negligible current drain from its source of power and is insensitive to large changes in the resistance of the said protective circuit. 